Metabolic engineering to enhance photosynthesis based on empirical data and in silico modelling

Lead Research Organisation: University of Essex
Department Name: Biological Sciences

Abstract

World demand for food is growing and it has been estimated that a 50% increase in yield will be needed to meet the increasing demand due to growing population. The changing climate and the competing demand for plants as biofuels further exacerbates this situation. Photosynthesis is the process by which plants use the energy from the sun to convert carbon dioxide from the atmosphere into carbohydrates and other chemical compounds, which are used for growth. Over the last decade numerous experiments of plants grown in elevated CO2 have shown unambiguously that increased rates of photosynthetic carbon assimilation can lead to increased biomass. Furthermore transgenic experiments conducted during the 1990's in which activities of individual enzymes were up- or down- regulated provided information showing that manipulation of the Calvin cycle could influence plant composition and increase plant productivity. These studies clearly identified photosynthetic carbon assimilation as an untapped opportunity to increase yield. In this project we will produce transgenic Arabidopsis plants with altered photosynthetic characteristics based on a combination of empirical data, metabolic and network modeling. A detailed physiological and molecular analysis of the resulting lines will carried out to obtain detailed measurements of photosynthetic parameters and growth in greenhouse grown plants. The transgenic plants generated in this programme with altered photosynthetic carbon metabolism will be used to explore the relationships between CO2 assimilation, carbon storage and plant growth. These analyses will provide data for further interrogation and improvement of these models. This research will also provide a proof of concept and will form the basis to enable informed manipulation of crop plants.

Technical Summary

Increasing demands of the growing world population for food and fuel are putting ever greater pressure on the need to develop higher yielding crop varieties. This goal must be achieved in a sustainable manner and in the face of elevated levels of CO2 and more extreme conditions of water availability and temperature. There is compelling evidence, from both transgenic studies and in silico kinetic modelling, that there is an opportunity to improve photosynthetic performance and that this can lead to significant increases in yield.
The overall aim of this project is to take an integrated approach using the knowledge gained from empirical analyses of transgenic plants and in silico studies from both metabolic and transcriptional network modelling, to produce plants with enhanced photosynthetic performance and increased yield.

1. Produce and verify transgenic plants with altered combinations of enzymes and proteins identified as targets from modelling and empirical studies.
2. Undertake physiological and molecular analysis of selected transgenic plants to obtain detailed measurements of leaf biochemistry, photosynthetic parameters and growth data in plants grown in well watered and water limiting conditions.
3. Refine the transcriptional and kinetic models based on analysis of transgenic plants. Use
the 'improved' models to identify further manipulations of photosynthetic carbon metabolism.

Planned Impact

WHO WILL BENEFIT FROM THIS RESEARCH?
The work is directly relevant to agriculture and for this reason the main non-academic beneficiaries of this research will be the agri-biotech commercial sector. In particular, the big four agri-businesses that have programmes to increase yield or alter composition of crop plants (Monsanto, Syngenta, Bayer AG, BASF Plant Science).

HOW WILL THEY BENEFIT FROM THIS RESEARCH?
One of the main challenges for such crop improvement programmes is identifying genetic targets that have a predictable impact on the metabolic output of interest. Often, metabolic manipulations in crop plants are hampered by metabolic compensation or unexpected and unwanted perturbations in linked areas of the metabolic network. This research may provide a data that can be used to improve and develop models to address these issues. This research will lead to a greater understanding of the factors limiting photosynthetic carbon metabolism. Effectively, one would be able to make major reconfigurations of metabolism and possible metabolic routes and this is likely to generate more predictable outcomes.
Ultimately, translation of this research into effective strategies for improving yield and composition of crops will benefit the UK economy (Sygenta, at least maintains a significant presence in the UK). Improved crop varieties will also be of benefit to UK agriculture and will help secure the security of food supply in the UK, thereby bringing substantial societal benefit.

WHAT WILL BE DONE TO ENSURE THAT THEY HAVE THE OPPORTUNITY TO BENEFIT FROM THIS RESEARCH?
We will endeavour to ensure that the companies mentioned above are aware of the research and its potential with respect to their yield programmes. We will open direct lines of communications with the relevant research directors in these companies at an early stage of the project and will provide them with regular updates of significant developments. This will be done by sending them 'executive summaries' of research progress and copies of any publications that result from the work. In addition, the PIs will visit the companies and give research seminars about the project.
 
Description We have shown that multigene manipulation of photosynthetic carbon metabolism can result in increased photosynthesis and biomass yield in model species.
Exploitation Route Our findings are now being translated into crop spaces e.g. SBPase has been shown in greenhouse grown wheat to increase grain yield and a field trial has been approved for the summer of 2017.
Sectors Agriculture, Food and Drink

 
Description Realising increased photosynthetic efficiency
Amount $45,000,000 (USD)
Organisation University of Illinois at Urbana-Champaign 
Sector Academic/University
Country United States
Start 09/2012 
End 09/2022
 
Title Enhancing Photosynthesis 
Description Previous studies have indicated that there is correlation between the capacity of electron transport and the content of the cyt b6f complex. Initially, cyt b6f inhibitors (Kirchhoff et al., 2000) and later transgenic anti-sense studies suppressing the accumulation of the RieskeFeS 20 protein (PetC), a key component of the cyt b6f complex (Price et al., 1995, 1998; Anderson et al., 1997; Yamori et al., 2011), both demonstrated a proportional relationship between linear electron flux and carbon assimilation in leaves, establishing a flux control coefficient close to one for the cyt b6f complex (Price et al., 1995; Kirchhoff et al., 2000). In addition, RNAi repression of PetM, one of the subunits of cytochrome b6f, resulted in a similar phenotype to 25 that shown with RNAi repression of Rieske iron sulphur protein (Hojka et al, Plant Physiology, August 2014, Vol. 165, pp. 1632-1646.) However, there has been no indication that overexpression of the Rieske iron sulphur protein can lead to increase photosynthesis rate and/or enhanced yield. Our work funded by this grant enabled us to provide a clear demonstration that overexpression of the Rieske FeS protein increases photosynthesis and biomass. 
IP Reference WO2017144901 
Protection Patent application published
Year Protection Granted
Licensed No
Impact none as yet
 
Description Cafe Scientifique Event 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Public/other audiences
Results and Impact A short presentation on the work undertaken in my laboratory including that funded by this project, the remainder of the session was a discussion.
Year(s) Of Engagement Activity 2013,2014
 
Description Open day 
Form Of Engagement Activity Participation in an open day or visit at my research institution
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Other audiences
Results and Impact Open day to celebrate 50th Anniversary of University
Year(s) Of Engagement Activity 2015